Effect of stretch on the isolated cat sinoatrial node

Abstract

Nodal tissue was removed from the cat heart under ether anesthesia and perfused in a specially constructed chamber with oxygenated Tyrode solution. Responses of the sinoatrial node cells of the cat heart to stretch were investigated by the use of floating microelectrodes to record activity in isolated nodal preparations. Stretch of the tissue accelerated the discharge rate and reduced cellular resting potential. Release of stretch gave the opposite effect. Within limits greater magnitudes of stretch caused greater responses. In some quiescent nodal cells, initiation of spontaneous discharge was induced by stretch. This propagated activity developed following a progressive reduction of resting potential and the appearance of subthreshold oscillations of the membrane potential subsequent to stretch. Restoration of a regular rate from an irregular rhythm was also seen. Atropine, neostigmine, and epinephrine had no significant effect but the acceleration response to stretch was suppressed somewhat by dichloroisoproterenol and augmented by cocaine. Perfusion with Tyrode solution containing K ion in +50 or -50% normal concentration did not greatly affect the degree of response although low K+ tended to delay the acceleration whereas high K+ gave the opposite effect. An increase in permeability to Na was thought to be involved in the stretch-produced acceleration of pacemaker action.